Biologically active natural products have played a key role in the elucidation of cellular processes and biological mechanisms, and have been fruitful sources of therapeutic agents for many decades. Nearly half of the new chemical entities introduced in drug discovery between 1981 and 2002 were natural products or semi-synthetic analogs of natural products. (Vasilevich, N. I., et al., J. Med. Chem. 2012, 55, 7003-7009.) Polypropionate tetrads and pentads comprise a core structural element of many biologically active natural products.